Todd Design-Build

    ADU Cost Estimator for Massachusetts

    How much does an ADU cost in Massachusetts? Get a real planning budget for a detached ADU, attached ADU, garage conversion, or basement ADU.

    Plan Your Budget

    Answer a few quick questions to get a ballpark cost range for your southeastern Massachusetts project—no commitment required.

    Step 1 of 617%

    What size ADU are you considering?

    Select the approximate living space you have in mind.

    ADU Cost Questions — Massachusetts

    How much does an ADU cost in Massachusetts?

    Most detached ADUs in Massachusetts run between roughly $350 and $500 per square foot all-in, plus site work. A typical 700–900 sq ft detached ADU lands in the $325,000–$475,000 range depending on site conditions, foundation type, sewer vs. septic, and finish level.

    How much does it cost to build a 1,000 sq ft ADU?

    A 1,000 sq ft detached ADU in southeastern Massachusetts typically prices between about $400,000 and $525,000 depending on foundation, utilities, and finishes.

    How much does a garage conversion ADU cost?

    Garage conversion ADUs are usually the most cost-effective path, often 20–35% cheaper than a comparable detached build because the shell already exists. Final cost depends on foundation upgrades, utilities, and code-required insulation and egress.

    Is this estimate a real quote?

    No — it's a planning range built from Todd Design-Build's actual Massachusetts pricing model. A firm quote requires a site walk and a preliminary plan set, which we handle as part of our design-build process.